Dedicated apparatus and method emission mammography

ABSTRACT

The present invention is an apparatus for examining a body part. The apparatus comprises a mechanism for immobilizing and compressing the body part. The apparatus also comprises a mechanism for providing an internal anatomical image of the body part and a mechanism for detecting single gamma-rays emitted by a radiotracer infiltrated into the body part. The detecting mechanism is disposed in an adjacent relationship with the mechanism for providing an internal anatomic image so that the body part remains in the same position during and between anatomic and radiotracer imaging. In one embodiment, the detecting mechanism includes a detector module disposed on one side of the immobilizing mechanism. The detector module preferably has at least one array of gamma ray sensitive material in communication with a position detector. In another embodiment, the detecting mechanism includes a pair of detector modules disposed one on each side of the immobilizing mechanism. The present invention is also an apparatus for examining a body part which comprises a mechanism for immobilizing and compressing the body part and a mechanism for providing a stereotactic internal anatomical image of the body part. The apparatus also comprises a mechanism for providing a stereotactic physiological image of the body part in an adjacent relationship with the mechanism for providing an internal anatomic image such that the body part remains in the same position during and between stereotactic anatomic and radiotracer imaging.

CROSS REFERENCE

This is a continuation application of U.S. patent application Ser. No.08/811,915 filed on Mar. 5, 1997, now U.S. Pat. No. 5,965,891 issued onOct. 12, 1999, which is a continuation of U.S. patent application Ser.No. 08/647,555 filed on May 14, 1996, abandoned, which is a continuationof U.S. patent application Ser. No. 08/262,737 filed on Jun. 20, 1994,now U.S. Pat. No. 5,519,221, which is a continuation-in-part of07/824,804 filed on Jan. 22, 1992, now U.S. Pat. No. 5,252,830.

FIELD OF THE INVENTION

The present invention is related to an apparatus for medicalexamination. More specifically, the present invention is related to anapparatus and method for imaging the radiotracer concentration in afemale breast or other organ.

BACKGROUND OF THE INVENTION

Mammography is currently the most effective method of screening forbreast cancer. The goal of breast cancer screening is the detection ofearly non-palpable tumors. Although mammography is very sensitive in thedetection of cancer, it is not very specific in determining whethermammographic abnormalities are due to benign or malignant disease(Limitations of Mammography in the Identification of NoninfiltratingCarcinoma of the Breast, S. F. Sener, F. C. Candela, M. L. Paige, J. R.Bernstein, D. P. Winchester, Surgery, Gynecology, and Obstetrics, Aug.1988, 167:135-140). Therefore, a noninvasive method of confirming themalignancy of suspicious mammographic abnormalities would be a majorbenefit in patient care. In this way, the number of benign excisionalbiopsies (approximately 75% of all excisional biopsies) can be reduced.

When abnormal mammograms are encountered, the physician's options arelimited. For minimally suspicious lesions, short-term repeat examination(four to six month follow-up) is often recommended. This may result inpsychological stress for the patient and introduces the possibility ofloss in patient follow-up due to scheduling or communication errors. Theunlikely possibility of interim tumor growth cannot be definitely ruledout (Breast Cancer: Age-Specific Growth Rates and Screening Strategies,M. Moskowitz, Radiolocy, Oct. 1986, 161:37-41), especially in patientsunder fifty.

The role of ultrasound in clarifying the status of a mammographicabnormality is limited to the differentiation of solid masses frombenign cysts. If the strict criteria for the ultrasonic appearance of asimple cyst are satisfied, the referring physician may be reassured thatthe lesion is benign. Unfortunately, the current spatial resolution ofultrasound makes the technique of limited value for lesionssignificantly smaller than five millimeters.

Doppler ultrasound has been advocated as a means for differentiatingbenign from malignant masses, but results of clinical trials have beencontradictory, and the doppler method has no current clinical role inbreast imaging (The Role of US in Breast Imaging, V. P. Jackson,Radiology, Nov. 1990, 177:305-311).

Fine-Needle Aspiration (FNA) of breast masses is a technique whosesensitivity and specificity is operator dependent (Fine-NeedleAspiration Biopsies of Breast Masses, L. Palombini et al., Cancer, Jun.1, 1988, 61:2273-2277), and has been considered experimental(Discriminating Analysis Uncovers Breast Lesions, D. B. Kopans,Diagnostic Imaging, Sept. 1991, pp. 94-101). Because of its relativelylow cost and reduced morbidity associated with surgery and anesthesia,FNA has been suggested as a possible replacement for excisional biopsy.Unfortunately, there is a high (13-50%) rate of insufficient sampleswhen FNA is performed on non-palpable mammographically detected lesions.All of these cases of negative FNAs require excisional biopsy(Fine-Needle Aspiration Cytology in Lieu of Open Biopsy in Management ofPrimary Breast Cancer, H. J. Wanebo et al., Annals of Surgery, May 1984,199 (5) pp. 569-579). Further, FNA as a non-imaging diagnostic modality,has the disadvantage that no information is obtained about the physicaldistribution of the detected tumor. As a cytopathological technique, FNAcannot easily differentiate between cases of marked dysplasia,carcinoma-in-situ, or invasive cancer. Fine-Needle Aspiration isgenerally not performed for non-palpable breast lesions.

Another option for the referral of a patient with equivocal mammographicanomalies is excisional biopsy of the breast in the area correspondingto the region of mammographic abnormality. The probability of malignancyranges from 2% for a circumscribed solid mass to almost 90% for aspiculated ill-defined mass (Discriminating Analysis Uncovers BreastLesions, D. B. Kopans, Diagnostic Imaging, Sep. 1991, pp. 94-101. Thetrue-positive fraction for biopsies obtained as a result of amammographic screening program is between twenty and thirty percent(Nonpalpable Breast Lesions: Accuracy of Prebiopsy MammographicDiagnosis, G. Hermann, C. Janus, I. S. Schwartz, B. Krivisky, S. Bier,J. G. Rabinowitz, Radiology, Nov. 1987 165:323-326; R. Brem, personalcommunication). Excisional biopsy has the additional disadvantage ofintroducing scarring, which may render interpretation of follow-upmammograms more difficult (Discriminating Analysis Uncovers BreastLesions, D. B. Kopans, Diagnostic Imaging, Sep. 1991, pp. 94-101). Anadditional disadvantage to excisional biopsies is that, as a non-imagingmodality, the physical distribution of the tumor is poorly described.

It is also possible to use radionuclide imaging to detect cancers.2-[F-18]-Fluoro-2-deoxy-D-glucose (FDG) is a radioactive analogue ofglucose that is taken up preferentially by cancer cells (Primary andMetastatic Breast Carcinoma: Initial Clinical Evaluation with PET withthe Radiolabeled Glucose Analogue 2-[F-18]-Fluoro-2-deoxy-D-glucose, R.L. Wahl, R. L. Cody, G. D. Hutchins, E. E. Mudgett, Radiology (1991)179:765-770). A Fluorine-18 nucleus decays by emitting a positron whichis annihilated within a millimeter by an electron. The result of thisannihilation is the production of two 511 kev (thousand electron volts)gamma rays that are approximately 180 degrees apart in direction. Aftera patient has received an intravenous dose of FDG she may be examinedwith detectors that sense these gamma rays.

Previous detection methods have included imaging with a speciallycollimated planar gamma camera ([18-F] Fluorodeoxyglucose scintigraphyin diagnosis and follow up of treatment in advanced breast cancer,European Journal of Nuclear Medicine (1989) 15:61-66) and with awhole-body Positron Emission Tomography (PET) scanner (Primary andMetastatic Breast Carcinoma: Initial Clinical Evaluation with PET withthe Radiolabeled Glucose Analogue 2-[F-18]-Fluoro-2-deoxy-D-glucose, R.L. Wahl, R. L. Cody, G. D. Hutchins, E. E. Mudgett, Radiology (1991)179:765-770). PET imaging of breast cancer patients given FDG has beenshown to be useful in imaging tumors as small as 3.2 cm and in patientswhose breasts are too dense to be imaged well mammographically (Primaryand Metastatic Breast Carcinoma: Initial Clinical Evaluation with PETwith the Radiolabeled Glucose Analogue2-[F-18]-Fluoro-2-deoxy-D-glucose, R. L. Wahl, R. L. Cody, G. D.Hutchins, E. E. Mudgett, Radiology (1991) 179:765-770).

The use of a specially collimated planar gamma camera to image thebreast with this high resolution is limited by technical factors. Theenergy of 511 KeV is too penetrating to be detected well by conventionalgamma cameras, and the collimation required to correct for the highenergy leads to loss of signal (counts/pixel) that is equivalent toresolution loss due to low photon flux.

Conventional PET imaging devices are designed to image cross sections ofthe entire body. Accordingly, there are several disadvantages toemploying a whole body PET scanner in a primary role as a highresolution confirmatory modality for small suspicious breast lesions.The first disadvantage of using a whole body PET scanner for breastimaging is the limited resolution available. The net resolution of awhole-body PET system is a combination of individual factors and islimited to above 5 mm FWHM (E. Rota-Kops et al., Journal of ComputerAssisted Tomography 1990, May-June 14 (3), pages 437-445; N. A. Mullaniet al., Journal of Nuclear Medicine 1990, May 31 (5), pages 610-616 andpages 628-631; K. Wienhard et al., Journal of Computer AssistedTomography 1992, Sep.-Oct. 16 (5) pages 804-813). The effect of thisresolution limit is that radioactivity is underestimated (PositronEmission Tomography and Autoradiography, Edited by M. E. Phelps, J. C.Mazziotta, H. R. Schelbert, pp. 240-285, Raven Press, N.Y. 1986; Designof a Mosaic BGO Detector System for Positron CT, H. Uchida, T.Yamashita, M. Iida, S. Muramatsu, IEEE Transactions on Nuclear ScienceFebruary 1986, NS-33 (1), pp. 464-467). This reduces the sensitivity ofPET scanners in estimating the malignancy of mammographically detectedlesions smaller than twice the resolution limit, and also precludes theuse of the PET scanner in delineating tumor margins with high accuracy.

A second disadvantage of a conventional PET scanner for imaging ofsubtle lesions in the breast is the high cost of the examination. Inorder to accommodate the entire body, a conventional PET scanner mustemploy tens or hundreds of expensive detector arrays along with a gantryand associated electronics.

A third disadvantage of a PET scanner is that the PET image format wouldnot be easily compared to conventional mammograms. This is due to thefact that the breast is an organ which can be compressed to anessentially two-dimensional object. The variability in internalarchitecture of the breast results in few landmarks for positioning, andthe location of an anomaly on the mammographic image of the compressedbreast does not always correspond to the same location in thenon-compressed breast.

In order to achieve the highest spatial resolution available in atomographic system, motion of the patient due to breathing must belimited. Immobilizing of the breast by compression is the moststraightforward approach to solving this problem, but implementationwithin a PET scanner detector ring is difficult. Additionally, the useof PET scanner to image an essentially two-dimensional object such as acompressed breast is not economically rational.

High resolution (20 cm diameter bore) PET scanners, originally developedfor animal studies, may soon be available commercially. For a systemwith smaller aperture (i.e. 20 cm bore for a dedicated head scanner) theresolution in the axial plane is 3.5 mm (Development of a HighResolution PET, T. Yamashita et al., IEEE Transactions on NuclearScience, April 1990, Vol. 37 (2) pp. 594-599). Such a system wouldsatisfy the goal of high resolution. A disadvantage would be theconsiderable cost of such relatively expensive scanners, withapproximately fifteen detector arrays, as dedicated units for breastimaging. Further, the problems of immobilization of the breast and ofcomparison to standard mammography would still be unaddressed.

SUMMARY OF THE INVENTION

The present invention is an apparatus for examining a body part. Theapparatus comprises means or a mechanism for immobilizing andcompressing the body part. The apparatus also comprises means or amechanism for providing an internal anatomical image of the body partand means or a mechanism for detecting single gamma-rays emitted by aradiotracer infiltrated into the body part. The detecting mechanism isdisposed in an adjacent relationship with the means or mechanism forproviding an internal anatomic image so that the body part remains inthe same position during and between anatomic and radiotracer imaging.

In one embodiment, the detecting means or mechanism includes a detectormodule disposed on one side of the immobilizing means or mechanism. Thedetector module preferably has at least one array of gamma ray sensitivematerial in communication with a position detector. In anotherembodiment, the detecting means or mechanism includes a pair of detectormodules disposed one on each side of the immobilizing means ormechanism. Preferably, the means or mechanism for providing ananatomical image includes an x-ray source and x-ray recording medium.

The present invention is also an apparatus for examining a body partwhich comprises means or a mechanism for immobilizing and compressingthe body part and means or a mechanism for detecting single gamma-raysemitted by a radiotracer infiltrated into the body part.

The present invention is also an apparatus for examining a body partwhich comprises means or a mechanism for immobilizing and compressingthe body part and means or a mechanism for providing a stereotacticinternal anatomical image of the body part. The apparatus also comprisesmeans or a mechanism for providing a stereotactic physiological image ofthe body part in an adjacent relationship with the means or mechanismfor providing an internal anatomic image such that the body part remainsin the same position during and between stereotactic anatomic andradiotracer imaging.

Preferably, the means or mechanism for obtaining a stereotacticphysiological image includes a pair of detector modules disposed one oneach side of the immobilizing means or mechanism. In one embodiment, thedetector modules are constructed to travel angularly about the body partto provide projection images of the body part from at least twodifferent viewing angles. In another embodiment, the detector modulesare stationary with respect to the body part and obtain multipleprojection views of the body part.

The present invention is also an apparatus for examining a body partwhich comprises means or a mechanism for immobilizing and compressingthe body part and means or a mechanism for providing a stereotacticphysiological image of the body part.

The present invention is also a method for examining a body part. Themethod comprises the steps of immobilizing the body part in a preferredposition such that the body part is compressed. Then there is the stepof obtaining at least one physiological image of the body part.Preferably, before the immobilizing step, there is the step of injectingthe patient with a radiotracer which emits gamma rays and the step ofobtaining at least one physiological image includes the step ofdetecting gamma-rays with at least one detector module disposed on atleast one side of the body part. If desired, after the step of obtainingat least one physiological image, there can be the step of directing abiopsy needle or gun into the body part 12 using at least onephysiological image for guidance and placement. After the step ofobtaining the image or images, there can then be the step of operatingon the patient using the image or images for guidance, localization, andpreferably confirmation that the tumor has been removed completely.After the operating step, there can be the step of obtaining at leastone image of surgical specimens to identify the presence of and theborders of tumors.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the preferred embodiment of the inventionand preferred methods of practicing the invention are illustrated inwhich:

FIG. 1 is a schematic representation of an apparatus for examining abody part.

FIG. 2 is a schematic representation showing a close-up view of thedetector modules of the apparatus for examining a body part.

FIGS. 3a and 3 b are schematic representations showing the arrangementof the sensor array on the Photomultiplier (PMT).

FIG. 4 is a schematic representation showing a plurality of imagingplanes between the detector modules.

FIG. 5 is a schematic representation of a gamma-ray stereotactic imagingapparatus with two gamma-ray detector modules configured for coincidencedetection or for dual-head single-emission acquisition.

FIG. 6 is a schematic representation of a gamma-ray imaging apparatuswith a gamma-ray detector module-configured for single-headsingle-emission acquisition.

FIG. 7 is a schematic representation of an x-ray stereotactic imagingapparatus.

FIG. 8 is a schematic representation of a gamma-ray stereotactic imagingapparatus with mobile detector arrays.

FIG. 9 is a schematic representation of a gamma-ray stereotactic imagingapparatus with stationary detector arrays.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals refer tosimilar or identical parts throughout the several views, and morespecifically to FIG. 1 thereof, there is shown an apparatus 10 forexamining a body part 12, such as a breast. The apparatus 10 includesmeans or a mechanism 14 for providing an anatomical image of the bodypart 12 and means or mechanism 16 for providing a physiological image ofthe body part 12. The means or mechanism 16 for providing aphysiological image is disposed adjacent to the means or mechanism 14for providing an anatomical image such that the body part 12 remains inthe same position during and between anatomical and physiologicalimaging. Preferably, the body part 12 is infiltrated with a radiotracerand the means or mechanism 16 for providing a physiological imageincludes means or a mechanism for detecting emissions of theradiotracers from the body part 12. The radiotracers can be2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) or 16alpha-[F-18]-fluoroestradiol-17 beta or other radiotracers. Preferably,the means or mechanism for providing an anatomical image includes anx-ray source and x-ray recording medium, such as x-ray film.Alternatively, a digital radiography device can be used. Alternatively,other methods of anatomic imaging such as magnetic resonance can beused. Alternatively, other methods of anatomic imaging such asultrasound can be used.

In a preferred embodiment, the radiotracer produces gamma rays and thedetecting means or mechanism includes two detector modules 20 each ofwhich has at least one sensor array 19 of gamma ray sensitive material(scintillator), such as bismuth germanate (BGO) crystals, mounted upon aposition detector 21 such as a photomultiplier array or positionsensitive photomultiplier. Alternatively, individual light sensors, suchas avalanche photodiodes can be mounted upon each gamma ray detector inthe array 19. In an alternative embodiment, each detector module 20 hasa continuous sheet of gamma ray detecting material which is mounted upona position sensitive multiplier or photomultiplier array. The continuoussheet of gamma ray sensitive material can have slots with septa on itssurface which would operate in a manner similar to the block detectorsknown in the art of PET scanners.

Preferably, each detector module 20 has dense shielding 23 for reducingundesirable emissions from other parts of the body. Preferably, eachdetector module 20 is attached to a swing arm 22 for allowing them toswing into and out of an operational portion. Preferably, the apparatus10 includes means or a mechanism 26 for immobilizing the body part 12,such as with compression. The immobilizing means or mechanism 26 caninclude a table 28 and a compression arm 30 which compresses the bodypart 12 against the table 28.

In an alternative embodiment, the apparatus 10 is not limited to havingmeans or a mechanism 14 for obtaining an anatomical image of the bodypart 12. The apparatus 10 includes means or mechanism 26 forimmobilizing the body part 12 and means or mechanism 16 for providing aphysiological image of the body part 12. The providing means ormechanism 16 is in an adjacent relationship to the immobilizing means ormechanism 26. Preferably, the immobilizing means or mechanism 26compresses the body part 12 and can include a table 28 upon which thebody part 12 rests and a compression arm 30 which compresses the bodypart against the table 28. Alternatively, the apparatus could include animmobilizing means or mechanism 26 consisting of a C-arm forintra-operative tumor localization.

The invention is also a method of examining a body part of a patient.The method includes the first step of immobilizing the body part in apreferred position. Then, there is the step of obtaining a physiologicalimage of the body part. Preferably, before the immobilizing step, thereis the step of injecting the patient with a radiotracer and theobtaining step includes the step of detecting emissions from theimmobilized body part. The step of obtaining an anatomical image of thebody part such as an x-ray can be performed before the immobilizingstep. Preferably, before the immobilizing step, there is the step ofperforming a compression examination, such as a spot view compressionexamination.

The invention is also related to an alternative method of examining abody part of a patient. This method includes the first step of obtainingan anatomical image of the body part. Then, there is the step ofobtaining a physiological image of the body part such that the body partremains in the same position during and between anatomical andphysiological imaging. Preferably, before the obtaining step, there isthe step of immobilizing the body part, such as with compression.

In the operation of the apparatus 10, a patient who is being examinedfor breast cancer would be injected with2-[F-18]-Fluoro-2-deoxy-D-glucose (FDG). FDG is a radiotracer which is aradioactive analogue of glucose that is taken up preferentially bybreast cancer cells. A more detailed explanation of this process isgiven in Primary and Metastatic Breast Carcinoma: Initial ClinicalEvaluation with PET with the Radiolabeled Glucose Analogue2-[F-18]-Fluoro-2-deoxy-D-glucose, R. L. Wahl, R. L. Cody, G. D.Hutchins, E. E. Mudgett, Radiology (1991) 179:765-770, incorporated byreference. The isotope 18-F decays by emitting a positron which isannihilated within a few millimeters by an electron. The result of thisannihilation is the production of two gamma rays that are approximately180° apart in direction.

Approximately one hour after injection with FDG, the patient undergoes aspot view breast compression examination. The breast 12 would then beimmobilized and a mammogram would be obtained for any areas suspiciousfor malignancy. If an abnormality is spotted on the mammographic film,high resolution detector modules 20 are swung in place above and belowthe compressed breast. Each detector module 20 consists of an array ofbismuth germanate crystals which detect the gamma rays produced by theFDG. Each array is mounted upon a position sensitive photomultiplier.Electronic collimation using coincidence gating would yield highsensitivity to emitted radiation. The shielding reduces the number ofundesirable emissions detected by the detector modules. Once thedetector modules 20 are swung into place an image of the emissions istaken in areas of suspicion.

The rationale for the apparatus is the adaptation of the standardradiological mammographic geometry for the detection of gamma raysproduced by positron-emitting and gamma-emitting radiotracers. Theapparatus would incorporate (or be easily mounted upon) a conventionalor x-ray mammography unit for straightforward comparison withconventional mammograms.

The increased sensitivity allowed by the mammographic geometry isexpected to permit imaging of suspicious areas in the breast within ashort period of time (10-15 minutes), allowing the patient to remain inbreast compression for the duration of the scan. Use of the inventionresults in exact registration between the conventional mammogram and theimage of radiotracer uptake. Advantages of the invention over existingtechnology include high resolution, low cost, reduced dose, anddecreased morbidity.

The proximity of the detector modules to the breast in the proposedmammographic geometry will lead to resolution superior even to highresolution PET scanners. Since image reconstruction via filteredbackprojection is not required in this geometry, no loss of resolutiondue to frequency filtering will be encountered.

The dose of radioactivity given to the patient will be similar to orless than the dose presently used for whole body PET imaging of FDG(approximately ten millicuries), which is within the acceptableradiation dose for diagnostic nuclear medicine techniques. The morbidityassociated with this dose must be compared to the morbidity associatedwith unnecessary excisional biopsy. For treatment planning, themorbidity may be compared to that associated with unnecessarymastectomy. For delineation of tumor margin, the morbidity should becompared to the local recurrence of tumor in an under-resected breast.

Positron emitters such as Fluorine-18 (half-life 110 minutes) can bepurchased by breast imaging centers from cyclotrons in most major U.S.cities. Note that the use of the proposed dedicated breast imagingdevice does not preclude the possibility of following the examinationwith a whole body PET scanner (if available) when clinically indicated,i.e., to search for metastases in a patient with proven cancer.Additionally, by placing a collimator upon one or both of the detectormodules, and operating the apparatus in a non-coincident mode, theapparatus could be used in conjunction with more generally availableradioisotopes that emit single photons. Additionally, the apparatuscould be taken to the operating room for intra-operative tumorlocalization.

If a radiotracer is used whose decay results in the production ofopposing gamma rays, such as 2-[F-18]-Fluoro-2-deoxy-D-glucose, thepresent invention envisions an apparatus 100 which is capable of3-dimensional imaging and offers optimal spatial resolution andsensitivity. As shown in FIG. 2, the apparatus 100 is comprised of afirst detector module 120 for detecting radiotracer emissions from thebody part 12 and a second detector module 121 for detecting radiotraceremissions from the body part 12. The first and second detector modules120, 121 are disposed adjacent to each other with the body part 12disposed therebetween. The apparatus 100 also comprises means or amechanism 102 for backprojecting detected coincident events with respectto the first and second detector modules 120, 121 onto a plurality ofimaging planes 132 between the first and second detecting modules 120,121. The imaging planes 132 are shown in FIG. 4.

Preferably, the first detector module 120 is comprised of a first sensorarray 122 of material sensitive to emissions from the radiotracer andthe second detector module 121 is comprised of a second sensor array 123of material sensitive to emissions from the radiotracer.

Preferably, as illustrated in FIG. 4, the backprojecting means ormechanism 102 comprises means or a mechanism for defining a line 130between a point on the first sensor array 122 and a point on the secondsensor array 123 associated with a coincident event and means or amechanism for determining the intersection of the line 130 with eachimaging plane 132. Preferably, the apparatus 100 also comprises means ora mechanism for determining the distance, d, and angle, a, between thefirst detector module 120 and the second detector module 121, such as aposition and angle encoder 136. Preferably, each of the first and seconddetector modules 120, 121 comprises a position detector, such as imagingPMT (photo multiplier) 108. Preferably, the apparatus 100 also comprisesmeans or a mechanism 104 for displaying the imaging planes such as adigital gamma camera display and acquisition system. Preferably, each ofthe sensor arrays 122, 123 are comprised of a large array of BGOcrystals (20×20 to 40×40).

The present invention is also a method of examining a body part 12. Themethod comprises the step of detecting a plurality of coincident eventsassociated with the interaction of radiotracer emissions from the bodypart 12 with a first and second sensor array 122 and 123. Then, there isthe step of backprojecting the detected coincident events onto aplurality of imaging planes 132 between the first and second sensorarrays 122 and 123.

Preferably, the backprojecting step includes the step of defining a line130 between a point of the first sensor array 122 and a second point ofthe second sensor array 123 associated with the coincident event anddetermining the intersection of the line 130 with each imaging plane132. Preferably, after the backprojecting step, there is the step ofdisplaying the plurality of imaging planes.

In the operation of the apparatus 100, the patient is injected with2-[F-18]-flouro-2-deoxy-D-glucose (FDG). As shown in FIGS. 3a and 3 b,each of the detector modules 120, 121 comprises a Hamamatsu R394I-02Imaging PMT 108 with an array 122, 123 of 37×37 BGO crystals above andbelow a breast 12. The width of each array 122, 123 is 75 mm, asrepresented by reference character A. Each crystal is 2×2×7 mm. The topof each crystal is cut at the optimal angle 250 to break the symmetry tomaximize the light collected by the PMT 108. The exact length (7 mmabove) is a compromise between efficiency and resolution. One wishes tomaximize the efficiency (make the crystals longer) while minimizing themultiple interactions which will blur the image (make the crystalsshorter) (“Single Interaction PET Detectors” C. A. Burnham, J. T.Elliot, D. E. Kaufman, D. A. Chesler, J. A. Correia, and G. L. Brownell.Conference Record of the 1990 IEEE Nuclear Science Symposium PP:1332-1336 1990, incorporated by reference.

This sensor array design is based on the belief that techniques whichwould measure the number of interactions are too complicated to bepractical (“Resolution and Sensitivity Improvement in Positron EmissionTomography by the First Interaction Determination” Z. H. Cho and S. C.Juh. IEEE 1991 Medical Imaging Conference (Santa Fe) Record pp.1623-1627). The effect of multiple interactions is reduced, by reducingthe probability of their occurrence. This thin sensor array design willhave reduced efficiency, but the other detection possibilities gained byallowing all crystals to be in coincidence will more than make up forthis. Oblique rays would normally require the measurement of the depthof interaction in each crystal to maintain good spatial resolution (“APET Detector with Depth-of-Interaction Determination” P. Bartzakos andC. J. Thompson. Phys. Med. Biol. V 36, pp. 735-748 (1991), but thesecrystals will be short enough to make this measurement unnecessary.Alternatively, a crystal block cut from the top and bottom with thebottom cuts offset from the top cuts by half the cut separation could beused to reduce the parallax error caused by oblique incidence on a deepdetector.

The first and second detectors modules 120, 121 are separable by raisingthe upper one. The distance, d, between them would be variable in orderto accommodate anatomical variations. The angle, a, between them wouldbe variable to accommodate imaging of organs such as the prostate, thatmight require non-parallel arrangement of the detector modules.

Each imaging PMT 108 would be connected to three analog-to-digitalconverters (ADCs) to measure the X and Y coordinates and the observedenergy of the gamma ray produced by the FDG radiotracer. The PMTs 108would be connected to a coincidence circuit and the backprojecting meansor mechanism 102 in order to detect the gamma rays produced by positronannihilations in the region between them. In principle coincidencesbetween any crystal in the first and second sensor arrays 122, 123 willbe permitted. It is from the diagonal coincidences, and the currentdetector module separation, d, and angle, a, that the depth of the eventcan be determined.

When an annihilation occurs between the first and second sensor arrays122, 123 the 511 keV gamma pair may travel in such directions that theywill interact with the first and second arrays 122, 123. As one rayenters a crystal it has a 20 to 30% chance of interacting with it,depending on the crystal depth and the photon direction. Of theseevents, 45% are photo-electric, depositing 511 keV in one crystal only.The shape of the crystals is such that most of the light photons createdin such events are detected by the PMT 108, making good energyidentification possible (Probably better than 10% full-width athalf-maximum [FWHM] energy resolution). The Compton scattered rays fromthe other 55% of the interactions will be scattered onto a cone whosemost probable apex angle is 45° and will deposit 50 keV in the crystalat a depth of 3 mm. The 461 keV ray will then escape and interact beyondthe crystal. For this reason the electronics for event detection shouldbe sensitive to the 511 keV photons from photo-electric events and25-150 keV photons corresponding to single Compton interactions of 511keV photons, and should be able to discriminate against the singleCompton interactions on the basis of their lower energy.

If two such photons (one in each detector module) are detected withinthe resolving time, a coincidence has occurred, and a line correspondingto the most probable depth of interaction in the two crystals iscalculated. This is done by using the effective detector separation, d,(see FIG. 2) and the coordinates of the crystals of the first and secondsensor arrays 122, 123 which interacted with the coincident rays.

With reference to FIG. 4, the coordinates of the crystal in the firstsensor array 122 is X_(U), Y_(U) and the coordinates of the crystal inthe second sensor array 123 is X_(L), Y_(L). The event is thus localizedon the line 130:

X_(i) =X _(L) +a _(i) (X _(U) −X _(L)) Y _(i) =Y _(L) +a _(j) (Y _(U) −Y_(L))   (1)

a _(i) =z _(i) /d . . . (i=1 to n)

It is not possible to determine the parameter a_(i), which would locatethe point of annihilation uniquely in 3-dimensional space. However, byassuming a value for a_(i) and thus defining an imaging plane 132, theX_(i) and Y_(i) coordinates could be determined for that imaging plane132. Supposing the detectors modules 120, 121 are 6 cm apart, 13 valuesfor a_(i) ranging from −3.0 cm to +3.0 cm are chosen. From equation 1,one can calculate 13 pairs (X_(i), Y_(i)) of coordinates whichcorrespond to the intersections of the line 130 given by equation 1 andthe imaging planes 132 defined by Z=−3.0 to Z=3.0 in 5 mm intervals.These sets of coordinates can now be considered as points in a 128 by128 by 16 matrix. All 16 of these matrix elements are augmented. [Onedoes not know where the event really occurred, but by assigning theevent (augmenting a memory location) at each level all possibilities areprovided for]. Augmenting a memory location means or mechanism to add asmall positive number to it. The magnitude of this number depends on therelative crystal pair efficiency, and the attenuation path length.

After placing the breast section to be examined between the twodetectors modules 120, 121, the first or upper detector module 120 islowered into place. The detector module separation, d, is measured witha position encoder 136. The position encoder 136 is read to calculate anangle scaling factor. Position determining look up tables are thencalculated and saved in the data acquisition system's processor's tableswhich are part of the backprojecting means or mechanism 102. Acquisitiontakes place for a preset time, some 30-50 minutes after the IV FDGinjection. When a coincidence is detected, the intersection points withpossible 13 imaging planes are calculated by looking in the tables. Theresulting 13 coordinates are presented to a modified gamma camerainterface, which is set up to do a gated study. The 13 coordinate pairsare presented in turn, as if they were in separate phases of the cardiaccycle. Thus, all imaging planes 132 are augmented, via aread-modify-write memory cycle. Preferably, the point of intersection ofthe line and each imaging plane is proportional to the photonattenuation along that line divided by the product of the crystals'relative sensitivities.

At the end of the study, the data can be displayed on display means ormechanism 104 with conventional gamma camera display software. Notethere is no reconstruction, as the memories contain the normalizedprojection data ready for display. Each imaging plane 132 contains animage of all data acquired throughout the study. The data has been, ineffect “back-projected” onto all 13 imaging planes, by adding the samenumber to different locations in each imaging plane 132.

An analogy can be made with conventional X-ray tomography in which anX-ray tube and film move in an elliptical motion above and below thepatient. The image is formed as an “in focus” image of the plane throughwhich a line joining the focal spot and one point on the film passesthrough the same point in the patient. Attenuation from other points isblurred by the relative motion. In the present invention, each imagingplane 132 contains data from annihilations which truly occurred nearthat plane, and all others. As in the case of the X-ray tomography, thedata which truly originated in that plane is in focus, that from otherplanes is blurred.

The 13 imaging planes 132 can now be examined one by one, or all can bedisplayed at once. The lower display threshold is raised until thebackground in normal tissue is almost “black”. At this point, “hotspots” will appear in regions of high glucose metabolism, and “coldspots” in regions of low glucose metabolism. For either cold or hotspots, the section which contains the highest contrast, or best definedboundaries, is the one which localizes the abnormality best.Conventional Gamma Camera software for smoothing, contouring,measurement of area, and enhancement can be used to process andinterpret the image.

Assuming that the same breast compression was used for a conventionalmammogram, the conventional and emission mammographic images can beregistered precisely.

To calibrate the apparatus 100, a plastic box having the dimensions ofthe largest compressed breast section likely to be imaged, is filledwith FDG solution. The normal scanning technique is used and the tableused to augment memory locations is filled with the value Ke^(μp) (whereμ is the linear attenuation coefficient for 511 keV gamma rays in water,0.098 cm⁻¹ and p is the geometrical path length. The crystal efficiencytables in memory are all set to “1”. Data is then acquired for about onehour.

At the end of the calibration scan all memory locations would have thesame number of counts if all path lengths were equal, and all detectormodules 120, 121 were equally efficient. They will have differentnumbers however due to counting statistics, and different crystal pairefficiencies. These will show up as variations in the calibrationimages. The line of response joining each crystal pair is then forwardprojected through all slices, and this is divided into the average valuefor all crystal pairs in order to derive the crystal efficiency table.

This calibration technique combines inter-crystal sensitivity andattenuation correction into the backprojection operation scaling, makingpossible real time image formation. The only difference is that ratherthan adding “1” to each memory location, a number which compensates forattenuation and inter-crystal sensitivity is added. Assuming the memorydepth is only 16 bits, this number must be scaled to preventquantization errors and over flows. It is anticipated that a number ofthe order of 100 would be used, with a range of 70 to 130. It may alsobe necessary to introduce a distortion correction as well in case theimaging response of the PMTs is nonlinear.

The apparatus 100 can be coupled to a minimally modified Gamma Cameraacquisition and display computer capable of gated studies. All thecalibration tables and line of response (LOR) calculations are selfcontained, but the highly developed Nuclear Medicine image processingsoftware is well suited for use with the apparatus 100.

The fact that no image reconstruction is required, but spatiallocalization in all three axes is possible by backprojecting scaledvalues along each LOR, mimicking a gated study. This simple techniqueprovides a simple imaging system with the best possible spatialresolution, and real time display of the images during formation. Asimilar approach to spatial localization has been discussed forapplications unrelated to breast imaging (Performance Parameters of aPositron Imaging Camera, by G. Muehlenner, M. P. Buchin, and J. H.Dudek, IEEE Transactions on Nuclear Science, Vol. NS-23, No. 1, February1976).

The present invention also envisions use of dedicated instrumentationfor emission mammography in conjunction with radiotracers that emitsingle gamma rays and/or photons. FIG. 5 shows a gamma-ray stereotacticimaging apparatus with two gamma-ray detector modules configured forcoincidence detection or for dual-head single-emission acquisition.Radiotracers that decay by positron emission result in the production ofa pair of gamma rays. Although such radiotracers are known to be highlyaccurate in the detection of breast cancer, recent reports in theliterature have supported a role for single photon, gamma ray emitterssuch as Technetium-99m (A. Waxman et al., Journal of Nuclear Medicine,Vol. 34, Issue 5, Page 139P). Advantages to using such emitters includelow cost and ease of availability as compared to positron emitters.

The apparatus 10 as described above would be adaptable for applicationto single photon emitters by using one or both of the detector modules20 to detect activity from the compressed breast. (See FIGS. 5 and 6.)

Coincidence circuitry would not be required for single emission systems.Note that reports are present in the literature (Lee et al., Journal ofNuclear Medicine, Vol. 34, Issue 12, Pages 2095-2099, and A. Waxman etal., Journal of Nuclear Medicine, Vol. 34, Issue 5, Page 139P,incorporated by reference herein) describe the use of gamma cameras todetect activity from the breast from single photon and positronemitters. The difference between these reports and the present inventionis that the present invention incorporates breast immobilization and/orcompression during acquisition of data. Several advantages are realizedas a result of this feature, which are enumerated as follows:

1. Since the breast contains few landmarks, internal details such astumors will not be reproducibly localized unlessimmobilization/compression is used. Reproducible localization isessential if the emission image is to be used for interventions such asbiopsy or placement of localizing needles for surgeons.

2. Immobilization/compression allows confident registration to beperformed with x-ray images, thereby increasing diagnostic confidence inthe ability of the emission image to characterize a lesion initiallydetected by x-rays.

3. Compression reduces the volume of tissue being imaged with thegamma-ray detectors to the region of clinical interest. This reductionin volume of tissue results in decreased attenuation of the gamma raybeam on its way from the lesion to the gamma-ray detector. Decreasedattenuation will lead to increased count density, which is advantageoussince the image is of higher diagnostic quality and since the dose tothe patient can be reduced.

As shown in FIG. 7, stereotactic guidance is a technique employed byradiologists to direct biopsies using x-ray images. The techniqueconsists of the acquisition of two projection images that differ inprojection angle. The data afforded by having the two images allows thedepth of a lesion to be assessed, just as the human brain can assess thedepth of an object by integrating information from both eyes. As appliedto mammography, the lack of internal stable structures in the breastrequire that the breast be immobilized during acquisition of bothprojections, without releasing compression between acquisitions. Severalmanufacturers (Fischer Corporation and Lorad Corporation) have designedmammography units in which software and display interfaces allow thestereotactic images to be inspected by a physician, and when a lesion isidentified on both views a computer calculates the expected depth of thelesion. When the coordinates of the lesion are generated by thecomputer, the physician can enter the coordinates into a biopsy gunmount so that biopsies of the lesion can be reliably obtained.

As is known in the art, biopsy guns incorporate hollow needle assembliesthat allow a core of tissue to be removed. Surgeons often request thathooks, needles, or dyes be placed in a suspicious lesion undermammographic guidance so that the surgeon can later identify the lesionin the operating room. Placement of such localizing hardware can beaccomplished using stereotactic guidance.

One application of the present invention to use stereotactic guidance toprovide projection images that can be used for stereotactic biopsyguidance. In a stereotactic x-ray mammographic unit (FIG. 7), the x-raydetector module travels a certain angle between the stereotactic views(usually 15 degrees) while the patient's breast 12 is under compression.In the present invention, as shown in FIG. 8, the gamma-ray detectormodules 20 can be positioned so as to travel a specified angle as well.

Alternatively, since the gamma cameras obtain information from manyprojections, it is possible to have the gamma ray detector modules 20remain in a single location while multiple projection views wereobtained for stereotactic guidance (FIG. 9). The projections obtainedfrom such projection views can be inspected by a human operator todetect a lesion. If the lesion is visible on more than one projectionview, calculations similar to those performed for x-ray stereotacticguidance can be performed to determine the depth of the lesion. Thecoordinates of the lesion can then be used to guide biopsy.

Heretofore, stereotactic guidance has never been done using gammacameras. The principal advantage of stereotactic guidance using gammaray imaging relates to the requirement for sampling or excising lesionswhich might be only detectable using gamma-ray imaging techniques. It isa medical dictum that a detection method is not helpful if the resultscannot be confirmed by biopsy, and current gamma cameras and positronemission tomography scanners are not well-suited to guide biopsies. Thisis due to the large size of these imaging devices and their relativelypoor detection efficiencies which necessitate long acquisitions times.The requirement that a patient remain in compression for acquisition ofthe stereotactic views and for biopsy implies that high quality imagesbe obtained in short times. The present invention allows this to happenbecause the detectors are so close to the breast, and becausecompression reduces the amount of attenuating tissue between the lesionand the detectors.

Note that the stereotactic capability of the invention allows biopsyguidance to be performed on the basis of the emission images alone or inconjunction with the x-ray images, since the gamma-ray detectors are inthe same geometry as the conventional x-ray detectors. Thus an area ofsuspicion by x-ray criteria could be localized by x-ray stereotacticguidance and the presence or extent of the lesion confirmed by gamma-rayimaging prior to biopsy. Alternatively, if no lesions were identifiableby x-ray criteria, and the emission images identified a suspiciouslesion, the biopsy could be guided on the basis of the emission imagesalone.

The present invention is an apparatus 10 for examining a body part 12.The apparatus comprises means or a mechanism 26 for immobilizing andcompressing the body part and means or a mechanism 14 for providing aninternal anatomical image of the body part. The apparatus also comprisesmeans or a mechanism for detecting single gamma-rays emitted by aradiotracer infiltrated into the body party in an adjacent relationshipwith said means or mechanism for providing an internal anatomic imagesuch that the body part 12 remains in the same position during andbetween anatomic and radiotracer imaging.

In one embodiment, as shown in FIG. 6, the detecting means or mechanismincludes a detector module 20 disposed on one side of the immobilizingmeans or mechanism 26. The detector module 20 preferably has at leastone array of gamma ray sensitive material in communication with aposition detector. In another embodiment, as shown in FIG. 5, thedetecting means or mechanism includes a pair of detector modules 20disposed one on each side of the immobilizing means or mechanism 26.Preferably, each detector module has at least one array of gamma-raysensitive material in communication with a position detector.Preferably, the means or mechanism 14 for providing an anatomical imageincludes an x-ray source and x-ray recording medium.

The present invention is also an apparatus for examining a body partwhich comprises means or a mechanism 26 for immobilizing and compressingthe body part and means or a mechanism for detecting single gamma-raysemitted by a radiotracer infiltrated into the body part 12. Thedetecting means or mechanism can include a detector module disposed onone side of the immobilizing means or mechanism or on both sides. Ifdesired, there can be included means or a mechanism for providing aninternal anatomical image of the body part, such as an x-ray device.

The present invention is also an apparatus for examining a body part 12which comprises means or a mechanism 26 for immobilizing and compressingthe body part 12 and means or a mechanism 100 for providing astereotactic internal anatomical image of the body part (FIG. 7). Theapparatus also comprises means or a mechanism 102 for providing astereotactic physiological image of the body part in an adjacentrelationship with the means or mechanism 100 for providing an internalanatomic image such that the body part remains in the same positionduring and between anatomic and radiotracer imaging.

Preferably, the means or mechanism 102 for obtaining a stereotacticphysiological image includes a pair of detector modules 20 disposed oneon each side of the immobilizing means or mechanism 26. In oneembodiment, as shown in FIG. 8, the detector modules 20 are constructedto travel angularly about the body part 12 to provide projection imagesof the body part 12 from at least two different viewing angles, as iswell known with x-ray stereotactic imaging. In another embodiment, thedetector modules 20 are stationary with respect to the body part 12 andobtain multiple projection views of the body part 12.

The present invention is also an apparatus for examining a body part 12which comprises means or a mechanism 26 for immobilizing and compressingthe body part and means or a mechanism 102 for providing a stereotacticphysiological image of the body part. As stated previously, detectormodules 20 can be positioned to travel angularly about the body part 12to provide projection images of the body part from at least twodifferent viewing angles or detector modules can be stationary withrespect to the body part 12 and multiple projection views of the bodypart are obtained to form a stereotactic image.

The present invention is also a method for examining a body part 12. Themethod comprises the steps of immobilizing the body part 12 in apreferred position such that the body part 12 is compressed andobtaining a stereotactic physiological image of the body part.Preferably, before the immobilizing step, there is the step of injectingthe patient with a radiotracer which emits gamma rays and the step ofobtaining a stereotactic physiological image includes the step ofdetecting gamma-rays with a pair of detector modules 20 disposed one oneach side of immobilizing means or mechanism. Preferably, before thestep of obtaining a stereotactic physiological image, there is the stepof obtaining a stereotactic internal anatomical image of the body part12. If desired, after the step of obtaining a stereotactic physiologicalimage, there can be the step of directing a biopsy needle or gun intothe body part 12 using the stereotactic physiological image for guidanceand placement.

Moreover, after the step of obtaining an image, for example, a singleimage or stereotactic images, there can be the step of operating on thepatient using the obtained radiotracer image or images for guidance andlocalization.

The present invention is also a method for examining a body part 12. Themethod comprises the steps of immobilizing the body part 12 in apreferred position such that the body part 12 is compressed andobtaining at least one physiological image of the body part. Preferably,before the immobilizing step, there is the step of injecting the patientwith a radiotracer which emits gamma rays and the step of obtaining atleast one physiological image includes the step of detecting gamma-rayswith at least one detector module 20 on at least one side of theimmobilizing means or mechanism. If desired, after the step of obtainingat least one physiological image, there can be the step of directing abiopsy needle or gun into the body part 12 using at least onephysiological image for guidance and placement. After the step ofobtaining the image or images, there can then be the step of operatingon the patient using the image or images for guidance, localization, andpreferably confirmation that the tumor has been removed completely.After the operating step, there can be the step of obtaining at leastone image of surgical specimens to identify the presence of and theborders of tumors.

Although the invention has been described in detail in the foregoingembodiments for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be described by thefollowing claims.

What is claimed is:
 1. A method for examining a body part comprising thesteps of: immobilizing the body part in a preferred position such thatthe body part is compressed; and obtaining stereotactic physiologicalimages of the body part.
 2. A method as described in claim 1 whereinbefore the immobilizing step, there is the step of injecting the patientwith a radiotracer which emits gamma rays, and the step of obtainingstereotactic physiological images includes the step of detectinggamma-rays with a pair of detector modules disposed one on each side ofthe immobilized body part.
 3. A method as described in claim 2 whereinbefore the step of obtaining stereotactic physiological images, there isthe step of obtaining a stereotactic internal anatomical image of thebody part.
 4. A method as described in claim 1 wherein after the step ofobtaining stereotactic physiological images, there is the step ofdirecting a biopsy needle or gun into the body part using thestereotactic physiological image for three-dimensional guidance.
 5. Amethod as described in claim 4 wherein after the step of obtainingstereotactic images, there is the step of operating on the patient usingthe obtained stereotactic image for guidance and localization.
 6. Amethod as described in claim 1 including after the step of obtaining theimage, there is the step of operating on the patient using the image forguidance, localization, and confirmation that any tumor of the body parthas been removed completely.
 7. A method as described in claim 6including after the operating step, there can be the step of obtainingat least one image of surgical specimens to identify the presence of andthe borders of tumors.
 8. An apparatus for examining a body partcomprising: a body part compressor; an anatomical imager; and aradiotracer imager including a gamma-ray detector for detecting singlegamma-rays emitted by a radiotracer infiltrated into the body part in anadjacent relationship with the internal anatomic imager such that thebody part remains immobilized during and between anatomic imaging andradiotracer imaging.
 9. The apparatus of claim 8 wherein the gamma-raydetector includes a detector module having an array of gamma raysensitive material in communication with a position detector.
 10. Theapparatus of claim 9 wherein the gamma-ray detector includes a pair ofdetector modules disposed one on each side of the body part compressor.11. The apparatus of claim 8 wherein the anatomical imager includes anx-ray source and an x-ray recording medium.
 12. The apparatus of claim 8wherein the body part compressor shields the detecting mechanism fromradiation emissions from other parts of the body.
 13. The apparatus ofclaim 8 wherein the shielding attenuates radiation emissions from otherparts of the body.
 14. The apparatus of claim 8 wherein the shieldingfilters radiation emissions from other parts of the body.
 15. Anapparatus for examining a body part comprising: a body part compressor;a stereotactic internal anatomical imager; and a stereotacticphysiological imager in an adjacent relationship with the internalanatomical imager such that the body part remains immobilized during andbetween anatomic imaging and physiological imaging.
 16. The apparatus ofclaim 15 wherein the physiological imager includes a pair of detectormodules disposed one on each side of the body part compressor.
 17. Theapparatus of claim 16 wherein the detector modules are disposed totravel angularly about the body part to provide projection images of thebody part from at least two different viewing angles.
 18. The apparatusof claim 16 wherein the detector modules are stationary relative to thebody part and wherein the detector modules obtain multiple projectionviews of the body part.
 19. An apparatus for examining a body partcomprising: a body part compressor; and a stereotactic physiologicalimager.
 20. The apparatus of claim 19 wherein the physiological imagerincludes a pair of detector modules disposed one on each side of thebody part compressor.
 21. The apparatus of claim 20 wherein the detectormodules are disposed to travel angularly about the body part to provideprojection images of the body part from at least two different viewingangles.
 22. The apparatus of claim 20 wherein the detector modules arestationary relative to the body part and wherein the detector modulesobtain multiple projection views of the body part to form a stereotacticimage.
 23. A method for examining a body part having a tumor defined bymargins comprising the steps of: immobilizing and compressing the bodypart; obtaining an internal anatomical image of the body part; obtainingstereotactic physiological images of the body part; and using theanatomical and physiological images to locate and delineate the marginsof the tumor in the body part.
 24. The method of claim 23 includingimmobilizing the body part during the anatomical and physiologicalimaging.
 25. The method of claim 23 further comprising the step ofintroducing a radiotracer to the body part to assist in physiologicalimaging of the body part.
 26. The method of claim 23 including obtainingthe physiological image using a detector that detects single gamma-raysemitted by a radiotracer infiltrated into the body part.
 27. The methodof claim 27 further comprising the steps of obtaining anatomical andphysiological images of the body part during removal of the tumor fromthe body part to confirm the absence of tumor in the body part after theremoval of the tumor.
 28. A method for examining a body part comprisingthe steps of: using the apparatus as described in claim 8 to compressand to obtain an image of a body part or portion thereof that has beenremoved from the body.